With reference to FIGS. 1A, 1B, and 1C, this sequence of views depicts various steps within a known injection molding process as executed on a known injection mold 8. FIG. 1A shows the injection mold 8 in a mold closed configuration just prior to injection of a molding material into a molding cavity 14 that is defined therein. FIG. 1B shows the injection mold 8 in the mold closed configuration after completion of a step of injecting the molding material into the molding cavity 14 to form a molded article 15. Lastly, FIG. 1C shows the step of opening of the injection mold 8 into a mold open configuration just prior to an ejection of the molded article 15 from a mold member 10.
The known injection mold 8 includes a melt distribution apparatus 40, a gate member 60, and the mold member 10. The melt distribution apparatus 40 is configured to fluidly connect an injection unit (not shown) with the molding cavity 14 for injecting, in use, the molding material therein via nozzle 20. The molding cavity 14 is definable between the gate member 60 and the mold member 10 when the injection mold 8 is arranged in the mold closed configuration (as shown in FIG. 1A). The gate member 60 is non-movably fixed to the melt distribution apparatus 40. A coolant channel 31 is defined in the gate member 60. The coolant channel 31 is connectable, in use, to a source and sink (not shown) of a coolant media for circulating a coolant therethrough to cool, in use, the gate member 60. The nozzle 20 includes a housing 37, a nozzle tip member 23, and a nozzle tip retainer 26. The nozzle tip retainer 26 cooperates with the housing 37 and the nozzle tip member 23 for coupling the nozzle tip member 23 to the housing 37. A heater 30 surrounds the housing 37 for a heating of the nozzle 20, in use, to maintain the molding material therein at a desired processing temperature.
The gate member 60 defines a pocket 62 that is configured to receive, in use, a forward portion of the nozzle 20 of the melt distribution apparatus 40. The forward portion of the nozzle 20 includes an exposed portion of the nozzle tip member 23 and a skirt portion 27 of the nozzle tip retainer 26. A nozzle interface 64 is defined at a boundary of the pocket 62. Likewise, the nozzle tip retainer 26 defines a gate interface 28 around an outer surface of the skirt portion 27. The nozzle interface 64 and the gate interface 28 are configured to cooperate in providing a sealing junction for preventing a leakage, in use, of a molding material therebetween. The nozzle interface 64 and the gate interface 28 are substantially non-movable (i.e. static) relative to each other when in use. In addition, a melt bubble 19 having a generally fixed volume is defined in a space that is provided between the pocket 62 and the forward portion of the nozzle 20. The gate member 60 further defines a gate passage that is configured to fluidly connect, in use, the melt bubble 19 with the molding cavity 14. The purpose of the melt bubble is to define a space that the molding material will fill and act as an insulating barrier to thermal conduction between the nozzle 20 and the gate member 60, which are heated and cooled, respectively, when in use.
A typical injection molding process includes a step of decompressing the melt distribution apparatus after completion of a hold portion (i.e. sustained melt pressure) of the step of injecting the molding material into the molding cavity 14. The foregoing step is executable by the injection unit wherein an injection piston (or a screw in a reciprocating-screw type of injection unit) is pulled back (i.e. retracted), whereby a suction is created that provides for relief of some of the residual pressure in the melt distribution components (e.g. a manifold—not shown, the nozzle 20, etc.) within the melt distribution apparatus. The step of decompressing is useful in conjunction with the operation of the melt distribution apparatus 40 wherein the nozzle 20 is configured to include a ‘hot-tip’ for sake of thermal gating. The construction and operation of the nozzle 20 is similar to that described in U.S. Pat. No. 6,609,902 to Blais et al., published on Aug. 26, 2003. Inadequate decompression of a thermally gated nozzle, particularly in conjunction with a short duration molding cycle, can lead to gate drool 17 as shown in FIG. 1C with the opening of the mold, wherein the residual pressure in the melt distribution components causes the flow out of a gate that is defined between the melt bubble 19 and the molding cavity 14. Decompressing of the melt distribution apparatus contributes to the molding cycle time.